MicroSquirt.com read only forum (Jan.15,2018)

Hey guys, we're having a problem when we are trying to crank our engine, the intake backfires out of one cylinder. It seems like something is wrong with the timing, and that one cylinder is sparking before the intake valves close. Our trigger offset is -351.00 degrees. We are using the stock vr crank sensor and hall effect cam sensor. We are using: trigger wheel teeth 12, missing teeth 0, skip teeth 12, delay teeth 0. We can get the engine to start and to idle, however like I said before, it backfires when cranking and sometime pops the throttle off from that one cylinder.

Any suggestions on what the problem could be?

What tuning software are you using....if TunerStudio, take some datalogs, look at the tooth triggering, and post a .msq.

Sometimes my engine can backfire when cranking, but this is usually poor battery voltage now. I did have problems at first because the engine was mistimed, and I was running too much advance. It could also be a noise issue, and possible resetting, but until you datalog we are all guessing.

As you are the competition I can't give out calibration maps, but I will share the basic setups to get you up and running with a uS and a Phazer.

Everything I'll mention is in here:
http://www.microsquirt.com/viewtopic.php?f=89&t=22851
But I will summarize:

First are you getting a reliable tach? This took changing some resistors in the uS for us. Easiest way is to scope out the VR+ and tachout, watch for false pulses on the tach side. http://www.microsquirt.com/download/file.php?id=5756

If you have a reliable tach, start a maximum speed data log. This will tell you if uS thinks it has missed a tooth or found extra tooth. What you may find is that things are erroring out due to the variability in RPM. This is caused by the decompression pin on the exhaust cam and the 180deg 2 cylinder. There is a version of the code (JT3) which Grippo modified for us to remove all error checking on timing. It has worked flawlessly since.

If you look closely in that thread you might just find a helpful attachment.

Good luck, See you in May.
Geoff

Feel free to PM me, if you need further assistance.